1. Field of the Invention
The present invention relates to an inclination angle metering apparatus for metering an inclination angle of a body of equipment with respect to a direction of gravity.
2. Related Background Art
FIG. 7 shows one example of a conventional inclination angle metering apparatus. In this apparatus, a beam of light Ls outgoing from a light source 101 is restricted in a predetermined shape (e.g., a slit- or pinhole-like shape) by a stop 102. The beam is converted to substantially collimated rays of light through a collimator lens 103 and falls on a prism 104. The beam Ls is incident at a predetermined angle of incidence (e.g., 45.degree.) on a liquid surface 106a via this prism 104. A transparent liquid 106 is sealed in a casing 107 above the prism 104. This prism 104 and the transparent liquid 106 both have substantially the same refractive index.
The beam Ls passing through the prism 104 is full-reflected by the liquid surface 106a of the liquid 106. The beam Ls reflected by the liquid surface 106a again penetrates the prism 104. The beam Ls is condensed through a condenser lens 108 on a light receiving element 109 such as a CCD line sensor or the like. A pattern of the stop 102 is formed on this light receiving element 109.
Now, let A be a condensing position on a light receiving element 109 when the equipment incorporating the abovementioned inclination angle metering apparatus is in a horizontal state. This position A is then stored. Even when the equipment is skewed, the horizontality of the liquid surface is always kept. Hence, it follows that the liquid surface is inclined (a state indicated by a broken line 106b in the Figure) to the equipment when viewed in a relative manner. Therefore, a light path of the beam reflected by a liquid surface 106b changes as indicated by a broken line Ls'. The condensing position on the light receiving element 109 shifts to a position B. This position B is detected, and the inclination angle is obtained based on a deviation from the previously stored position A.
The conventional inclination angle metering apparatus, however, presents the following drawback. If the optical system and the light receiving element which constitute this inclination angle metering apparatus are minutely shifted in placement due to vibrations and impacts or variations in temperature, etc., then even when in the horizontal state, it the condensing position on the light receiving element shifts from the position A described above. Consequently, an error is caused in the metered inclination angle. Note that in this connection, the error is also produced even when the liquid surface is relatively inclined.